x86_x64 not booting on my PC

i have hp dc7900 (core2duo E8400). i tried using portable x64 etcher but after successfully writing, boot files are missing. no start.elf, bootcode.bin,etc. only recalbox-boot.conf on the main. BOOT folder contain "grub" folder, bzImage, initrd.gz, EFI folder contain BOOT folder with bootx64.efi & grub.cfg. I cannot boot it even if I disable "data execution prevention" on the bios. No secure boot setting on my bios. I also tried disabling my main hard drive and only USB drive is set to boot. Should I use the old recalbox version, I saw a youtube video (a year old) that has different boot files than the latest recalbox? Need help please. Thanks

@zhidd can you explain how to use plop ?
i have the same PC (SFF dc 7900 ) with a Sapphire HD5450. I do not manage to boot on USB Stick with last Recalbox :(
I try to boot with plpbt.img on usb Stick...but nothing.
Thx.